Suppression and Extinguishment of Boundary Layer Flame over Communication Cable by `Gas-like' Water Mist in Cross-flow

Abstract

Fire suppression experiments are performed with `gas-like' water mist in cross-flow on bare (without PVC jacket) communication cables to simulate a worst-case scenario. As fine water droplets are injected at low velocities, an initial envelope flame that engulfed the circumference of the cable recedes and forms a wake flame stabilized behind the cable. At high-mist concentration and/or high-air velocity, the flame is extinguished by shrinking rather than blowing-off, which is the case in flat plate boundary layer flames. The results show that ultra fine mist (UFM, Sauter mean droplet diameter, SMD = 3 μm) seems to be more effective in reducing the extinguishment time than high-pressure spray nozzle mist (SMD = 20 μm), which introduces spray-induced turbulence. The cable flame is extinguished rapidly after a threshold UFM concentration is exceeded. The threshold concentration decreases with increased air velocity. Finally, the copper cylindrical mesh, which is part of the cable, significantly enhances the effectiveness of UFM in flame extinguishment.